1. Field of the Invention
The present invention relates to a magneto-resistance effect head for reading information signals recorded in a magnetic recording medium, and a magnetic storage device employing the head.
2. Description of the Related Art
A magneto-resistance effect head (hereinafter, referred to as an MR head) is equipped with a magneto-resistance effect element (hereinafter, referred to as an MR element) whose electric resistance value changes as a function of the intensity and direction of a magnetic flux, and detects the electric resistance value of the MR element to detect a magnetic field signal. This MR head operates based on the anisotropic magneto-resistance effect (hereinafter, referred to as an AMR effect), and can read data from the surface of a magnetic body at a large linear density. The AMR effect is an effect that one constituent of the resistance of the MR element changes in proportion to the square of the cosine of the angle between the magnetization direction and the direction of the sense current flow inside the MR element. The AMR effect is explained in detail in the paper titled xe2x80x9cMemory, Storage, and Related Applicationsxe2x80x9d written by D. A. Thompson and others, IEEE Trans. on Mag. MAG-11, P1039 (1975).
In the MR head using the AMR effect, in order to suppress Barkhausen noise, a vertical bias magnetic field is applied in many cases. As a material for a vertical bias layer for applying the vertical bias magnetic field, anti-ferromagnetism materials such as FeMn, NiMn, and Nickel oxide are used.
Furthermore, recently, a more conspicuous magneto-resistance effect has been found wherein changes in the resistance of the MR element are dependent on the spin-dependent transmission of conductible electrons between magnetic layers interposed by a nonmagnetic layer and spin-dependent scattering at the layer interface accompanying the transmission. This magneto-resistance effect is known by various names such as xe2x80x9cGiant magneto-resistance effectxe2x80x9d or xe2x80x9cSpin-valve effectxe2x80x9d. Since such an MR element has greater changes in the resistance accompanying changes in the magnetic field than that of the MR element using the AMR effect, the sensitivity is improved. In this MR element, the resistance within a plane between a pair of ferromagnetic layers separated by a nonmagnetic layer changes in proportion to the cosine of the angle between the magnetization directions of the two ferromagnetic layers.
For example, in Japanese Patent Application Laid-open No. 2(1990)-61572, a lamination magnetic structure is disclosed for the purpose of realizing high MR changes by making the magnetization directions alternately in reverse to each other and in parallel with each other inside the magnetic layers due to the spin-valve effect. As materials that can be used in this lamination structure, ferromagnetic transition metals and alloys are proposed in the Application. Furthermore, a lamination structure whereby one of at least two ferromagnetic layers separated by a middle layer is provided with a fixing layer for fixing the magnetization direction of the ferromagnetic layer, and a lamination structure whereby the FeMn is used as a material for the fixing layer are disclosed.
In addition, in Japanese Patent Application Laid-open No. 4(1992)-358310, for the purpose of improving the sensitivity of the MR element upon adding the AMR effect and the spin-valve effect, an MR element is disclosed, which has two ferromagnetic thin layers separated by a nonmagnetic metal thin layer, and in which the magnetization directions of the two ferromagnetic thin layers become orthogonal to each other in the case where an applied magnetic field is zero. The resistance between the two ferromagnetic layers changes in proportion to the cosine of the angle between the magnetization directions of the two ferromagnetic layers due to the spin-valve effect, which has no connection with the direction of current flowing inside the MR element.
However, in these prior-arts, since the composition of the MR element is so complicated that reduction in size of the MR element is limited, and therefore, it is difficult to improve the recording bit density.
Therefore, in Japanese Patent Application Laid-open No. 11(1999)-175920, in an MR compound head employing a ferromagnetic tunnel joint, a structure is disclosed, in which the lower magnetic shield is simultaneously used as the lower electrode, and the upper magnetic shield is simultaneously used as the upper electrode. In accordance with omission of the upper and lower magnetic gap that results from simultaneous use of the lower magnetic shield as the lower electrode and the upper magnetic shield as the upper electrode, the space between the upper and lower magnetic shields can be narrowed. Therefore, the recording bit density can be improved in principle.
However, there are problems in the structure disclosed in Japanese Patent Application Laid-open No. 11(1999)-175920 as follows. An MR element using the spin valve effect or ferromagnetic tunnel joint has a basic component in which a fixing layer, a fixed magnetic layer, a nonmagnetic layer or insulation barrier layer, and a free magnetic layer are laminated in this order, wherein the free magnetic layer is disposed at the end part of the basic component. Since magnetic shields are provided at both sides of this basic component, the free magnetic layer is directly contacted with the magnetic shield or disposed at a distance close to the shield via a thin protection layer. Therefore, a leak magnetic field from a magnetic recording medium that flows into the free magnetic layer as a magnetism sensing portion is absorbed by the magnetic shields and becomes smaller. Furthermore, a static magnetic field and a sense current magnetic field generated from the magnetic layers comprising the MR element are also absorbed by the magnetic shields, and the bias point of the MR element easily deviates from the designed value.
The abovementioned problems are solved to some degree if the lower magnetic shield layer or upper magnetic shield layer contacted with the free magnetic layer is made to be sufficiently thick. However, in such a case, in the process of manufacturing the MR head, the patterning of the thick lower magnetic shield layer or thick upper magnetic shield layer is carried out together with the basic component portion comprised of the fixing layer, fixed magnetic layer, nonmagnetic layer or insulation layer, and free magnetic layer. Therefore, in a case where the upper magnetic shield layer is made thick, the milling depth when patterning increases, so that control becomes difficult. When the lower magnetic shield layer is made thick, re-adhering matter occurred when milling of the lower magnetic shield layer increases, so that it is easier for the fixed magnetic layer and free magnetic layer to become short-circuited. In a case where the patterning of the upper magnetic layer and the patterning of the basic component portion are carried out in different processes and the upper shield pattern is formed to be smaller than the pattern of the basic component portion, if anything, the form of the MR element becomes wrong and the element characteristics deteriorate since the patterning of only the upper magnetic shield layer is difficult.
An object of the present invention is to improve reproduction performance of an MR head having two electrodes-cum-magnetic shield layers without increasing the thickness of the electrodes-cum-magnetic shield layers.
A magneto-resistance effect head according to the present invention comprises a magneto-resistance effect element which has a free magnetic layer, the magnetization direction of which changes depending on applied magnetic fields, a nonmagnetic layer, a fixed magnetic layer, the magnetization direction of which is fixed, and a fixing layer for fixing the magnetization direction of said fixed magnetic layer, and the resistance value of the magneto-resistance effect element changes depending on applied magnetic fields. Also, the magneto-resistance effect head has a first electrode-cum-magnetic shield layer which is disposed at the free magnetic layer side of the magneto-resistance effect element and functions as an electrode and a magnetic shield of the magneto-resistance effect element, a second electrode-cum-magnetic shield layer which is disposed at the fixing layer side of the magneto-resistance effect element and functions as an electrode and a magnetic shield of the magneto-resistance effect element, and a magnetic gap adjusting layer which is made of a non magnetic conductor and provided between the free magnetic layer and first electrode-cum-magnetic shield layer. The first and second electrodes-cum-magnetic shield layers, free magnetic layer, nonmagnetic layer, fixed magnetic layer, and fixing magnetic layer are laminated in one direction.
In the present invention, without contacting the electrodes-cum-magnetic shield layer and the free magnetic layer, a magnetic gap adjusting layer is provided between them, whereby the free magnetic layer which is a magnetism sensing portion for leak magnetic fields can be spatially separated from the electrodes-cum-magnetic shield layer. Thereby, since sufficient leak magnetic fields flow into the free magnetic layer, the reproduction sensitivity is increased and the reproduction output is improved. In addition, the shield proximity effect on the magnetostatic coupling between the free magnetic layer and fixed magnetic layer and sense current can be eliminated, so that design of the bias structure to provide an optimum operating point becomes easier. As a result, an output waveform having excellent waveform symmetry without distortion can be obtained.
Also, in the present invention, provision of two electrodes-cum-magnetic shield layers which function both as electrode layers and magnetic shield layers allows high recording density, and the manufacturing yield is excellent since the thickness of the electrodes-cum-magnetic shield layers are not increased.
A protection layer may be interposed between the free magnetic layer and magnetic gap adjusting layer. The protection layer is called an undercoat layer or upper base layer, and is provided for the purpose of improving adhesion. Furthermore, as the nonmagnetic layer, an insulation barrier layer may be used to form a tunnel joint layer.
Another magneto-resistance effect head according to the present invention comprises a lower electrode-cum-magnetic shield layer, a magnetic gap adjusting layer which is made of a nonmagnetic conductor and formed on the lower electrode-cum-magnetic shield layer, a pair of vertical bias layers formed on the magnetic gap adjusting layer with interposition of a space, a free magnetic layer which is formed in the space on the magnetic gap adjusting layer so that both ends are contacted with the vertical bias layers, and changes its magnetization direction depending on applied magnetic fields, a nonmagnetic layer formed on the free magnetic layer, a fixed magnetic layer formed on the nonmagnetic layer, the magnetization direction of which is fixed, a fixing layer which is formed on the fixed magnetic layer to fix the magnetization direction of the fixed magnetic layer, an insulation layer formed so as to fill the surrounding of the fixed magnetic layer and fixing layer, and an upper electrode-cum-magnetic shield layer formed on the insulation layer and fixing layer.
Still another magneto-resistance effect head according to the present invention comprises a lower electrode-cum-magnetic shield layer, a fixing layer formed on the lower electrode-cum-magnetic shield layer, a fixed magnetic layer which is formed on the fixing layer and whose magnetization direction is fixed by the fixing layer, a nonmagnetic layer formed on the fixed magnetic layer, a free magnetic layer which is formed on a part of the nonmagnetic layer and changes its magnetization direction depending on applied magnetic fields, an insulation layer formed so as to fill the surrounding of the free magnetic layer, a pair of vertical bias layers which is formed on the insulation layer so as to be contacted with both ends of the free magnetic layer and applies a magnetic field to the free magnetic layer, a magnetic gap adjusting layer which is formed on the pair of vertical bias layers and free magnetic layer and composed of a nonmagnetic conductor, and a upper electrode-cum-magnetic shield layer formed on the magnetic gap adjusting layer.
The magnetic storage device according to the present invention comprises a magnetic recording medium, a magneto-resistance effect head for reproducing information recorded in the magnetic recording medium, an inductive head for recording information onto the magnetic recording medium, an actuator for positioning a magnetic head comprised of the magneto-resistance effect head and inductive head on the magnetic recording medium, and a control unit for controlling the actuator and magnetic head. In addition, the magneto-resistance effect head comprises a magneto-resistance effect element, which has a free magnetic layer, the magnetization direction of which changes depending on applied magnetic fields, a nonmagnetic layer, a fixed magnetic layer, the magnetization direction of which is fixed, and a fixing layer for fixing the magnetization direction of the fixed magnetic layer, and whose resistance changes depending on applied magnetic fields. The magneto-resistance effect head comprises a first electrode-cum-magnetic shield layer which is disposed at the free magnetic layer side of the magneto-resistance effect element and functions as an electrode and a magnetic shield of the magneto-resistance effect element, a second electrode-cum-magnetic shield layer which is disposed at the fixing layer side of the magneto-resistance effect element and functions as an electrode and a magnetic shield of the magneto-resistance effect element, and a magnetic gap adjusting layer which is made of a nonmagnetic conductor and provided between the free magnetic layer and first electrode-cum-magnetic shield layer. The first and second electrodes-cum-magnetic shield layers, free magnetic layer, nonmagnetic layer, fixed magnetic layer, and fixing layer are laminated in one direction.